<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>test</title>
    <script type="text/javascript">
        // 1.NaN
        if(NaN) {
            alert("NaN is " + true);
        }
        else{
            alert("NaN is " + false);
        }
        // 2.""
        if("") {
            alert("'' is " + true);
        }
        else{
            alert("'' is " + false);
        }
        // 3.[] is true
        if([]) {
            alert("[] is " + true);
        }
        else{
            alert("[] is " + false);
        }
        // 4.undefined
        var variable;
        if(variable) {
            alert("undefined is " + true);
        }
        else{
            alert("undefined is " + false);
        }
        // 5.null
        if(null) {
            alert("null is " + true);
        }
        else{
            alert("null is " + false);
        }
        // 6.0
        if(0) {
            alert("0 is " + true);
        }
        else{
            alert("0 is " + false);
        }
    </script>
</head>
<body>
</body>
</html>